Partially crosslinked elastomeric polymers and process for producing the same

ABSTRACT

A partially crosslinked, unsaturated elastomeric polymer of a C 4  to C 7  isomonoolefin and a C 4  to C 14  conjugated multiolefin is provided which has a low crosslink density. The partially crosslinked polymer is produced by curing an uncrosslinked unsaturated polymer having a low level of chemically bound halogen with a curing agent which reacts only with the halogen. Processes for preparing these partially crosslinked unsaturated polymers are also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to crosslinked elastomeric polymers havinga relatively low density of crosslinks, that is, a partially crosslinkedunsaturated elastomeric polymer.

2. Description of Information Disclosures

Crosslinked elastomers are known in which the molecular chains arecrosslinked at the sites of the carbon to carbon double bond, of theuncrosslinked initial polymer, as well as at the site of otherfunctional groups present in the uncrosslinked polymer, such as, forexample at the site of chemically-bound halogen.

Partially crosslinked polymers are known such as those disclosed in U.S.Pat. Nos. 2,781,334 and 2,729,626 in which the polymers are prepared bycopolymerizing an isoolefin with a conjugated diolefin and a divinylbenzene. Such polymers require the use of divinyl benzene in itspreparation as well as the use of the isoolefin and the conjugateddiolefin. A brochure of Polysar Corporation discloses Polysar® ButylTerpolymers such as XL 10,000 (previously XL-20), including Polysar®Butyl Terpolymer XL 40302 which is described as a halogenated type(printed in Canada, 1988).

Halogenated butyl rubber having a low level of halogen e.g., chlorinecontent of about 0.5 mole percent (about 0.3 wt.%) and a low level ofnon-halogenated isoprene unsaturation are disclosed in a paper entitled"Chlorobutyl Designed for Curing Members" authored by J. V. Fusco, I. J.Gardner, P. Hous and D. S. Tracey presented at a meeting of the RubberDivision, American Chemical Society, Mexico City, Mexico, May 9-12,1989.

Numerous patents disclose halogenated butyl rubber containing variousamounts of chemically bound halogen, for example, U.S. Pat. No.2,631,984 discloses brominated butyl rubber containing at least 0.5weight percent bromine; U.S. Pat. No. 2,732,354 discloses chlorinatedbutyl rubber containing from 0.4 to 2.3 weight percent chlorine; U.S.Pat. No. 3,099,644 discloses a process for the continuous halogenationof butyl rubber to produce a halogenated rubber containing 1.13 weightpercent chlorine. U.S. Pat. No. 2,732,354 discloses chlorinated butylrubber containing from about 0.4 to 2.3 weight percent of chlorine. U.S.Pat. No. 2,944,578 describes compositions comprising chlorinated butylrubber in which the butyl rubber has been substitutively chlorinated tocontain at least 0.5 weight percent chlorine; FIG. II of this patentappears to include a data point at about 0.6 wt.% chlorine. U.S. Pat.No. 3,099,644 discloses a process for the continuous halogenation ofbutyl rubber to produce a halogenated rubber containing 1.13 weightpercent chlorine. U.S. Pat. No. 2,943,664 discloses adhesivecompositions for tire cords comprising chlorinated butyl rubbercontaining at least 0.5 percent by weight of combined chlorine. U.S.Pat. No. 2,964,489 discloses a process for the production of tubelesstires and curing bladders containing 0.5 weight percent chlorine. Thechlorine content of known chlorinated butyl rubber is typically definedby a formula, as shown, for example, in U.S. Pat. No. 2,964,489 (column2, lines 50-60) and expressed as being "at least 0.5 wt. percent(preferably at least about 1.0 wt. percent) combined chlorine." In arestatement of the chlorine concentration, it is stated that thereshould be "at least 0.2 and preferably at least about 0.5 weight percentof combined chlorine in the polymer." (id, lines 60-62).

U.S. Pat. No. 4,130,534 discloses elastoplastic compositions comprisinga blend of thermoplastic crystalline polyolefin resin and a butylrubber, crosslinked to the extent that it is at least 90 percent gelled.It defines butyl rubber (at column 5, lines 17-34) to include"copolymers of isobutylene and isoprene containing 0.5 to 10, morepreferably 1 to 4 percent by weight isoprene and said copolymershalogenated with from 0.1 to about 10, preferably 0.5 to 3.0 weightpercent chlorine or bromine which chlorinated copolymer is commonlycalled chlorinated butyl rubber".

U.S. Pat. No. 3,758,643 and U.S. Pat. No. 3,862,106 (W. K. Fischer)disclose a partially crosslinked EPDM polymer having a gel content of atleast 30 percent but less than 90 percent by weight as measured byimmersion in cyclohexane for 48 hours at 73° F.

It is known to perform melt phase reaction of polymers in continuousflow devices, such as extruder-reactors. See, for example, U.S. Pat.Nos. 4,513,116; 4,548,995; 4,554,326, and 4,563,506, the teachings ofwhich are hereby incorporated by reference.

U.S. Pat. No. 4,594,390 discloses the use of an extruder to preparethermoplastic compositions comprising a blend of plastic and curedrubber.

There is field of use for butyl rubber wherein the rubber itself isrequired to be uncured, but where the inherent properties of uncuredrubber (cold flow, low green strength) represent a drawback. Such usesinclude those where butyl and halobutyl are the polymeric material ineasily processed formulations suitable for mastics, pipe wrap, sealants,cable fillers etc. Formulations based on such uncured rubbers tend toflow in service, and therefore, it would be useful to employ in suchformulations butyl or halobutyl rubber which has been partially cured.

The disadvantages associated with known partially cured butyl rubberderive from the manner in which such polymers are produced and the meansfor crosslinking which are employed. For example, known partiallycrosslinked butyl is produced by adding to the butyl compound, undercuring conditions, a curative such as a sulphur or phenol resin systemin an amount which is less than the amount required to give crosslinkingat all of the available crosslinking sites. The result is a vulcanizedrubber which is crosslinked through some of the unsaturation sites inthe copolymer backbone. However, because such unsaturation sites arerelatively numerous, and because the process is limited by dispersion ofthe curatives in the polymer, it is extremely difficult to control thecrosslinking. The result is a product with a reduced unsaturation andwith inconsistent product quality deriving from the failure to controlthe extent and location of crosslinking within and between the polymerchain. Similar problems arise when the starting polymer, prior tocrosslinking, is known halobutyl rubber, since in this case the halogenatoms carried on the isoprene units also contribute to the crosslinkingmechanism, making control even more difficult.

An alternative way to obtain partially cured butyl rubber is tointroduce a crosslinking agent such as divinyl benzene into the reactorin which the copolymerization is carried out. Again, though, the degreeand distribution of crosslinking along the copolymer chains is difficultto control, and the product, therefore, suffers from variability in itsproperties.

It has now been found that elastomeric polymers can be produced whichhave a controlled relatively low degree of crosslinking, therebyconstituting useful products which can be used where uncured rubbershave been used but without the disadvantages of uncured rubber. Thepartially crosslinked elastomeric polymers of the present invention canbe further processed in conventional rubber processing equipment and areuseable in such formulations as adhesives, sealants, etc. The partiallycrosslinked elastomeric polymers of the invention possess elastomeric aswell as thermoplastic properties.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a partiallycrosslinked, unsaturated copolymer of a C₄ to C₇ isomonoolefin and a C₄to C₁₄ conjugated multiolefin, comprising substantially randomlydistributed covalent crosslinks, an olefinic unsaturation ranging fromabout 0.05 to about 5.0 mole percent, a gel content ranging from about10 weight percent to about 90 weight percent as measured in cyclohexanefor 48 hours at a temperature of 23° C., said crosslinks having beenformed after the polymerization and halogenation of the correspondinguncrosslinked copolymer of a C₄ to C₇ isomonoolefin and a C₄ to C₁₄conjugated diene, said crosslinked unsaturated copolymer beingsubstantially free of chemically bound halogen.

In accordance with the invention, there is also provided a process forpreparing a partially crosslinked unsaturated copolymer of a C₄ to C₇isomonoolefin and a C₄ to C₁₄ conjugated multiolefin, which comprisesthe step of contacting, at crosslinking conditions, an uncrosslinked,unsaturated halogen-containing copolymer of a C₄ to C₇ isomonoolefin anda C₄ to C₁₄ conjugated multiolefin comprising an unsaturated,non-halogen-containing moiety and an unsaturated, chemically boundallylic halogen-containing moiety, said halogen being selected from thegroup consisting from about 0.05 to about 0.4 weight percent chlorine,from about 0.05 to 0.5 weight percent bromine and mixtures thereof, inthe presence of a curing agent which reacts essentially only with saidallylic halogen and in the absence of a curing agent which reacts withsaid unsaturated, non-halogen-containing moiety.

DETAILED DESCRIPTION OF THE INVENTION

The partially crosslinked, unsaturated copolymers of a C₄ to C₇isomonoolefin and C₄ to Cl₄ conjugated multiolefin of the presentinvention have covalent crosslinks which are randomly distributed and anolefinic unsaturation ranging from about 0.05 to about 5.0 mole percent,preferably from about 0.50 to about 2.5 mole percent, more preferablyfrom about 0.10 to about 2.0 mole percent. The gel content of thecrosslinked unsaturated copolymers of the invention ranges from about 10wt.% to about 90 wt.%, preferably from about 10 to about 89 wt.%, morepreferably from about 40 to about 85 wt.% as measured by soaking asample of the material in cyclohexane for about 48 hours at about 23° C.In any event, the gel content of the crosslinked copolymer, will begreater than the gel content of the uncrosslinked copolymer prior to thecrosslinking reaction. The crosslinks are formed after thepolymerization of the isomonoolefin with the conjugated multiolefin andafter the halogenation thereof. The crosslink density of the totalcrosslinked polymer may range from about 0.05 to about 0.22×10⁻⁴ molesper cubic centimeter, preferably from about 0.10 to about 0.18×10⁻⁴moles per cubic centimeter. The crosslink density of the polymer isdetermined by equilibrium solvent swelling using the Flory-Rehnerequation, J. Rubber Chem. and Tech., 30, p. 929. The appropriate Hugginssolubility parameter for butyl rubber/cyclohexane, 0.433 used in thecalculation was obtained from the review article by Sheehan and Bisio,J. Rubber Chem and Tech., 39, 167.

The crosslinked copolymers of the present invention are substantiallyfree of chemically bound halogen. By the term "substantially free ofchemically bound halogen" is intended herein, a crosslinked copolymercomprising less than about 0.1 weight percent chemically bound halogen,preferably less than about 0.06 wt.% chemically bound halogen.

The average molecular weight between crosslinks (Mc) of the crosslinkedunsaturated elastomeric polymers of the invention as calculated from thecrosslink density and the equation ##EQU1## may range from about 100,000to about 20,000 which is equivalent to from about 0.05 to about 0.22moles of crosslinks per cm³.

PROCESS FOR THE PREPARATION OF THE CROSSLINKED UNSATURATED ELASTOMERICPOLYMERS

The partially crosslinked, unsaturated copolymers of the presentinvention are prepared by contacting an uncrosslinked, unsaturatedhalogen-containing polymer of a C₄ to C₇ isomonoolefin and a C₄ to C₁₄conjugated multiolefin comprising at least one unsaturated monomericmoiety which does not have a chemically bound halogen and at least oneunsaturated moiety which has a chemically bound allylic halogen with acuring agent which reacts essentially only with the allylic halogen andin the absence of a curing agent which reacts with the unsaturatedmonomeric moiety which does not have a chemically bound halogen, such asfor example, in the absence of a phenolic resin and in the absence ofelemental sulfur, for a time sufficient to form covalent crosslinks atthe allylic halogen sites.

Suitable curing conditions include a temperature ranging from about 100°to 260° C., preferably from about 170° to 210° C., for a time periodranging from above zero to about 15 minutes. The pressure is notcritical.

The curing agents, which are useful in the practice of the invention,include metal oxides of Groups IIB, and IVA of the Periodic Table ofElements, such as zinc oxide; zinc salts of organic compounds such aszinc salts of dithiocarbamic acid, for example, zincdibutyldithiocarbamate, zinc dimethyldithiocarbamate; amines;dimercaptans, diols, thiourea-thiurams, alkyl phenol disulfides, andother dithiocarbamates, and mixtures thereof. A preferred curing agentcomprises zinc oxide. More preferably, the curing agent comprises zincoxide and a zinc salt of dithiocarbamic acid.

The Periodic Table of Elements referred to herein is in accordance withthe table published by Sargent-Welch, copyright 1968, Sargent-WelchScientific Company.

The curing agent may be used in combination with accelerators orco-curing agents such as fatty acids, for example, stearic, palmitic,lauric acids; weak amines, salts of these two groups; polyalcohols;aminoalcohols e.g., triethanolamine; ethylene glycol; diamines; zinccarbonate, etc.

It is important to conduct the curing step of the present invention inthe absence of a curing agent which could react effectively with thenon-halogenated unsaturated moiety of the uncrosslinked initialcopolymer to prevent crosslinking a t the unsaturated sites(carbon-to-carbon double bond) of the non-halogenated unsaturatedmoiety.

Suitable amounts of curing agent to be used in the process of thepresent invention include a molar ratio of curing agent to bound halogenin the uncrosslinked (halogenated) initial polymer of at least 0.25:1,preferably at least about 1:1. The upper limit is not critical and maysuitably be 10:1, preferably 7:1 more preferably 5:1.

If desired, the uncrosslinked (halogenated) polymer is contacted atconditions, (e.g., including a sufficient time period) for the curingagent to react with substantially all the chemically bound halogen ofthe initial uncrosslinked polymer and, thereby, produce a covalentlycrosslinked polymer substantially free of chemically bound halogen.

It should be noted that polymers comprising a low level of crosslinkshave, heretofore, been obtained by using low proportion of curing agentsso that crosslinks will not be formed at all available reactive sites(e.g., halogen and unsaturated sites) in the polymer chain. Sincecontrol of curative concentration, dispersion, etc., is difficult, theproducts obtained by such control of the concentration of the curingagent are not usually consistent in their level of crosslinks and areless preferred.

An advantage of the process of this invention is to attempt to crosslinkas many of the halogen sites as feasible. Such a process is reproduciblewhereas attempting to crosslink only a portion of the halogen isdifficult to reproduce. The curing agent of the present invention may beused in stoichiometric excess over the chemically bound halogen of theinitial uncrosslinked polymer. Since use of the curing agent of thepresent invention results in crosslinks only at the halogen sites, it isthe halogen concentration which controls the crosslink density of thecrosslinked polymer product of the invention.

An advantage of using a curing agent in stoichiometric excess is that itis possible theoretically to remove substantially all the halogenmoieties from the initial uncrosslinked polymer, either because thehalogen sites are crosslinked, or because they have been substituted bya curative moiety or consumed in a side reaction.

The curing step may be conducted under static conditions, for example,in an autoclave, a curing press etc., or under dynamic conditions, e.g.,in an extruder or internal mixer.

The contacting zone for the curing step of the present invention may bein an internal mixer and may be a batch-wise or continuous process,(e.g.), (Banbury®, Brabender® or extruder type). Preferably, the initialuncrosslinked polymer and the curing agent are contacted at curingconditions in a continuous flow device. Suitable devices includekneaders, extruders (employing single or multiple screws, e.g., twinscrews), continuous mixers and a blending/extrusion device referred toas a cavity transfer mixer as described in U.S. Pat. No. 4,419,014, theteachings of which are hereby incorporated by reference.

The initial uncrosslinked halogen-containing unsaturated polymers

The initial uncrosslinked halogen-containing unsaturated polymerssuitable for use in the curing step of the process of the presentinvention include halogen-containing copolymers of a C₄ t o C₇isomonoolefin and a C₄ to C₁₄ multiolefin (i.e., halobutyl polymers).The uncrosslinked halogen-containing copolymer comprises: (1) at leastone, but generally more than one, unsaturated monomeric moiety which hasa carbon to carbon double bond (olefinic unsaturation) and which doesnot have a chemically bound halogen atom, and (2) at least one, butgenerally more than one, unsaturated monomeric moiety which comprises acarbon to carbon double bond and a chemically bound allylic halogen,that is, a halogen atom attached to the allylic carbon atom. Thecopolymer additionally comprises a C₄ to C₇ isomonoolefin moiety.

The chemically bound halogen may be chlorine, bromine and mixturesthereof. The chemically bound halogen may be present in theuncrosslinked initial copolymer in an amount ranging from about 0.05 toabout 0.4, preferably from about 0.05 to about 0.39, more preferablyfrom about 0.1 to about 0.35 weight percent chlorine or from about 0.05to about 0.5, preferably from about 0.05 to about 0.49, more preferablyfrom about 0.1 to about 0.45 weight percent bromine and mixturesthereof. When mixtures of halogen are employed, the bromine contentlimits apply except that the chlorine content should not exceed about0.4 weight percent. The total unsaturation of the initial uncrosslinkedhalogen-containing unsaturated polymers may suitably range from about0.05 to 5, preferably from about 0.50 to 2.5, more preferably from about0.10 to 2.0 mole percent.

The halogen-containing copolymer of an isomonoolefin and a multiolefinare obtained by the halogenation of a copolymer of a C₄ to C₇isomonoolefin and a C₄ to C₁₄ multiolefin, hereinafter referred to as"butyl rubber".

The useful copolymers comprise a major portion of isomonoolefin and aminor amount, preferably not more than 30 wt. percent, of a conjugatedmultiolefin. The preferred copolymers comprise about 85-99.5 wt. percent(preferably 95-99.5 wt. percent) of a C₄ -C₇ isomonoolefin, such asisobutylene, and about 15-0.5 wt. percent (preferably about 5-0.5 wt.percent) of a multiolefin of about 4-14 carbon atoms. These copolymersare referred to in the patents and literature as "butyl rubber"; see,for example, the textbook Synthetic Rubber by G. S. Whitby (1954 editionby John Wiley and Sons, Inc.), pages 608-609 etc. The term "butylrubber", as used herein, includes the aforementioned copolymers of anisomonoolefin having 4-7 carbon atoms and about 0.5 to 20 wt. percent ofa conjugated multiolefin of about 4-14 carbon atoms. Preferably thesecopolymers contain about 0.5 to about 5 percent conjugated multiolefin.The preferred isomonoolefin is isobutylene. Suitable conjugatedmultiolefins include isoprene, butadiene, dimethyl butadiene,piperylene, etc. The preferred conjugated multiolefin is isoprene.

Commercial butyl rubber is a copolymer of isobutylene and minor amountsof isoprene. It is generally prepared in a slurry process using methylchloride as a vehicle and a Friedel-Crafts catalyst as thepolymerization initiator. The methyl chloride is liquid at -100° C. andoffers the advantage that AlCl₃, a relatively inexpensive Friedel-Craftscatalyst is soluble in it, as are the isobutylene and isoprenecomonomers. Additionally, the butyl rubber polymer is insoluble in themethyl chloride and precipitates out of solution as fine particles thatthereby forms a slurry. The polymerization is generally carried out attemperatures of about -90° C. to -100° C. See U.S. Pat. Nos. 2,356,128and 2,356,129 incorporated herein by reference.

The polymerization process, which is typically carried out in a drafttube reactor, is continuous. Monomer feed and catalyst are continuouslyintroduced at the bottom of the draft tube where an axial flow pump islocated. The pump circulates the slurry at high velocity to provideefficient mixing and heat transfer. Polymer slurry containing about20-30 wt. percent butyl rubber continuously overflows from the reactorthrough a transfer line.

Where the desired product is the butyl rubber itself, the slurry is fedthrough the transfer line to a flash drum operated at about 140-180pa(1.38-1.58 atm) and 65°-75° C. Steam and hot water are mixed with theslurry in a nozzle as it enters the drum to vaporize methyl chloride andunreacted monomers which pass overhead, are recovered, and the polymeris finished by water removal and drying. Where, however, it is desiredto produce a halogenated butyl rubber, this can be accomplished bypreparing a solution of the rubber. Generally, any halogenationtechnique may be utilized, including solution halogenation and meltphase halogenation.

In one preferred method of halogenation, a "solvent replacement" processis utilized. Cold butyl rubber slurry in methyl chloride from thepolymerization reactor is passed to an agitated solution in a drumcontaining liquid hexane. Hot hexane vapors are introduced to flashoverhead the methyl chloride diluent and unreacted monomers. Dissolutionof the fine slurry particles occurs rapidly. The resulting solution isstripped to remove traces of methyl chloride and monomers, and broughtto the desired concentration for halogenation by flash concentration.Hexane recovered from the flash concentration step is condensed andreturned to the solution drum.

In the halogenation step of the process, butyl rubber in solution iscontacted with chlorine or bromine in a series of high-intensity mixingstages. Hydrochloric or hydrobromic acid is generated during thehalogenation step and must be neutralized. For a detailed description ofthe halogenation process see U.S. Pat. Nos. 3,029,191 and 2,940,960, aswell as U.S. Pat. No. 3,099,644 which describes a continuouschlorination process, all of which patents are incorporated herein byreference.

The uncrosslinked halogen-containing initial copolymers suitable for usein the curing step of the present invention may be obtained byhalogenating an uncrosslinked unsaturated butyl rubber having aconcentration of unsaturation which falls within the desired previouslystated ranges for the initial halogenated uncrosslinked polymer.

The low concentration of halogen in the halogenated butyl rubber can beachieved by alternative means. In one method of preparation, the butylrubber containing a low concentration of double bonds, e.g., by means ofenchained isoprene, is halogenated in a 1:1 molar ratio, therebyincorporating approximately one halogen atom for each double bondoriginally present in the butyl rubber. Alternatively, butyl rubbercomprising a concentration of such double bonds greater than is requiredbased on the preferred concentration of halogen, is only partiallyhalogenated, thereby retaining unhalogenated double bond moieties. Wherepartially halogenated butyl rubber is used, the concentration ofunhalogenated double bonds is generally from about 0.12 to about 1.88mole percent; preferably from about 0.12 to about 0.75 mole percent.

DESCRIPTION OF THE PREFERRED PREPARATION PROCESS EMBODIMENT

A preferred embodiment for the process of preparation of crosslinkedcopolymers of the invention is to perform the crosslinking in aextruder-reactor. A more preferred embodiment of the process is asfollows:

An uncrosslinked unsaturated halogenated elastomeric polymer comprisingfrom about 0.05 to about 0.4 wt.% chemically bound chlorine or fromabout 0.05 to about 0.5 wt.% chemically bound bromine is introduced intoa extruder- reactor comprising various operating zones such as:

(A) Feed Zone--in which the uncrosslinked halogenated copolymer isintroduced into the extruder-reactor in convenient form. This formincludes, for example, particles and/or pellets. A solvent or diluentmay also be introduced into the feed zone. The feed zone is designed toform the polymer feed into a cohesive mass and convey or pump the masspast a restrictive dam which may follow the feed zone and distinguishesit from the reaction zone which follows.

This operation is generally conducted at low shear and temperaturesconsistent with the desired result and at a pressure sufficient toconvey the mass, typically up to about 600 psig, preferably up to about400 psig, most preferably up to about 200 psig. Lower pressures arepreferred in order to avoid overheating the polymer. This can beachieved, e.g., by utilizing an extruder screw with relatively with deepflights and by keeping the length of the feed zone, i.e., the feed zonescrew length, as short as possible commensurate with desired productionrates. For example, polymer is introduced at a temperature ranging fromroom temperature to about 200° C. and exits from the feed zone at about60° to 200° C.

A restrictive dam may be used to separate the feed zone from thereaction zone which follows it. This dam is not restrictive enough,however, to cause excessive overheating of the polymer. A restrictivedam can be, for example, a reverse flighted screw section, a filledscrew section, a shallow flighted screw section, an unflighted screwsection, combinations thereof, or other means known in the art. If anunflighted screw section is employed, it can have a larger diameter thanthe root diameter upstream of it, for example, 5 to 25 percent larger,but not greater than the screw flight diameter. The restrictive damlength should be about 0.5 to about 23 screw diameters, preferably about1 to about 2 screw diameters, more preferably about 0.5 to about 1 screwdiameters in length. If a reverse flighted screw section is in employed,it can be single or multi-flighted, preferably multi-flighted.

It should be noted that where the restrictive dam configuration employedis more than a mere separation boundary or region between zones, forexample, more than merely an unflighted screw section, the restrictivedam can be considered to be part of the reaction zone itself, forexample, when a single or multi-flighted reverse flighted screw sectionis employed. Under such circumstances, the restrictive dam in thisregion of the extruder-reactor can be a part of or comprise a reactionzone. When the reaction zone is operated under vacuum in a partiallyfilled mode, the restrictiveness of the dam between the feed andreactions zones can be reduced so as to permit some gas (e.g., air) toflow into the reaction zone from the feed zone.

In addition to the copolymer which is introduced into the feed zone, anoptional diluent may also be added. A diluent can function to reduce theviscosity of the copolymer to a level commensurate which subsequent goodmixing without the necessity for excessive heat and risk of molecularweight breakdown and undesirable side reactions; it can also function toreduce the temperature of the polymer. The diluent may be volatilesaturated higher hydrocarbons, chlorohydrocarbons or chlorocarbon suchas pentane, hexane, methylene chloride, chloroform or carbontetrachloride. It may also be a non-hydrocarbon readily removable fromthe system downstream, but able to perform the function of temporarilyreducing the apparent viscosity of the copolymer in the reaction zone.Materials added with the rubber, including diluents and/or curatives canbe facilitated in their dispersion in the rubber by including aconveying zone or section preceeding the reaction zone.

(B) Reaction Zone--is the zone in which the halogenated uncrosslinkedpolymer is heated at a temperature ranging from about 100 to about 260C, preferably from about 170° to about 210° C., for a time sufficient toproduce the desired partially crosslinked polymer of the presentinvention. The residence time in the reaction zone will generally rangefrom above 0 to about 3 minutes, preferably from about 1 to about 2minutes.

A curative agent, such as, for example, zinc oxide and zincdibutyldithiocarbamate is also present in the reaction zone. Thecurative agent may be introduced into the reaction zone by variousmeans. Thus, the curative agent may be pre-dispersed at the desiredconcentration in the uncrosslinked polymer at the desired concentrationor it can be introduced as a separate stream into the feed zone and orinto the reaction zone.

Also important for achieving efficient reaction of the copolymer is theincorporation in the reaction zone of means to produce the level ofcopolymer mixing and surface disruption preferred for the practice ofthis invention. This can be achieved, for example, by utilizing reverseflights on the reaction zone portion of the extruder screw, pins,shallow flights, etc. Other means include operation of the screw at arotation rate of about 50 to 600 RPM, preferably about 70 to about 400RPM, most preferably about 70 to about 200 RPM and by incorporation of adownstream restrictive dam of the type described above, to separate thereaction zone from the zone which follows it.

(C) Sweep Zone--preferably the extruder-reactor comprises a sweep zonein which entrained air and any volatile reaction products are swept outof the extruder. Suitable means to effect removal of these materials isthe injection of an inert gas into the extruder. Vent means are providedin this zone to permit inert gas and disengaged materials to be sweptout and removed from the system. In a particularly preferred embodiment,the screw configuration in the region of the vent comprises a deepsingle flighted screw with little or no mixing occurring in the vicinityof the vent in order to avoid restricting the exiting flow of inert gasand disengaged materials. If desired, stabilizers and other additivesmay be added to the copolymer in this sweep zone. Multiple injectionsites can be used as well as a supplementary injection zone.

(D) Exit Zone--Preferably the extruder-reactor comprises a final exitzone in which the temperature of the partially crosslinked polymerproduct is adjusted for delivery at a temperature, for example, belowabout 200° C., more preferably below about 150° C. and most preferablybelow about 100° C. as a contribution to the stability of the copolymer.Also in the exit zone, stabilizers may be added to the polymer product.

The partially crosslinked unsaturated polymer which is produced in theextruder-reactor may be recovered as such or further processed toproduce a desired shape, such as bales, pellets, etc.

The following examples are presented to illustrate the invention. Unlessotherwise indicated, all parts and percentages are by weight.

EXAMPLE 1

The following uncrosslinked halogenated butyl rubbers were used asinitial polymers for the preparation of crosslinked polymers of thepresent invention:

Polymer A was a copolymer of isobutylene and isoprene having about 0.8to 1.0 mole percent unsaturation and 0.28 wt.% chemically boundchlorine, a Mooney viscosity (1+8) at 125° C. of 57 as measured inaccordance with test ASTM D-1646. Polymer A also contained 0.98 wt.%calcium stearate which was used in its preparation.

Polymers B and C were uncrosslinked copolymers of isobutylene andisoprene having 0.9 mole percent unsaturation, a Mooney viscosity at125° C. of 57-58. Polymers B and C had different chlorine levels.Polymer B contained 0.23 wt.% chemically bound chlorine. Polymer Ccontained 0.18 wt.% chlorine.

Four different curative packages were incorporated into the lowhalogenated uncrosslinked Polymers A, B, and C. The amounts andformulation of the curative packages are shown in Table 1. Theproportions given in Table 1 are parts by weight based on 100 parts byweight of the uncross-linked low halogenation initial polymers.

                  TABLE 1                                                         ______________________________________                                        Curative packages                                                                          I   II         III   IV                                          ______________________________________                                        ZDEDC.sup.(1)  1.5   1.5        --  --                                        ZDBDC.sup.(2)  --    --         2   2                                         ZnO            3     3          0.5 --                                        Stearic Acid   0.5   0.5        --  --                                        MgO            0.5   --         --  --                                        ______________________________________                                         .sup.(1) ZDEDC  denotes zincN-diethyl dithiocarbamate                         .sup.(2) ZDBDC  denotes zincN-dibutyl dithiocarbamate                    

In each case, the blend was produced in a Banbury® mixer by the steps of(1) placing 100 parts of low halogen content uncrosslinked polymer intothe mixer at room temperature and heating with mixing at 150° C. over 6minutes; (2) then adding the curative package to the mixer in theindicated amounts and mixing for an additional 7 minutes whilecontrolling the mixer cooling and shear rate to maintain the blend at150° C.; and (3) dumping the blend at 150° C. after a total time in themixer of 13 minutes.

The curing process described above was monitored by reproducing themixing on a Brabender® plastograph. The Brabender® results are shown inTable 2.

                  TABLE 2                                                         ______________________________________                                               Initial                                                                             Maximum           Maximum                                               Torque                                                                              Torque    Scorch  Torque  Blend                                         (Nm)  (Nm)      Time    Time    Color                                  ______________________________________                                        Curative II                                                                   Polymer C                                                                              25      30         1'   3'30"   white                                Polymer B                                                                              25      30        20"   2'      white                                Polymer A                                                                              25      30        imme- 1'      white                                                           diate                                              Curative III                                                                  Polymer C                                                                              27      34         1'   3'30"   white                                Polymer B                                                                              25      30        40"   2'06"   white                                Polymer A                                                                              25      31        imme- 1'12"   white                                                           diate                                              Curative IV                                                                   Polymer C                                                                              28      32         2'   5'30"   clear                                Polymer B                                                                              27      32         2'   4'30"   clear                                Polymer A                                                                              25      31         1'   4'18"   clear                                ______________________________________                                    

The crosslinked blends produced as described above were subjected toMooney viscosity measurement at 150° C. (1+8 minutes) in accordance withASTM test 1646. The results are shown in Table 3, in which values inparenthesis are for the blends produced in the Brabender mixer; othervalues are for blends produced in the Banbury mixer.

                  TABLE 3                                                         ______________________________________                                        CURATIVE PACKAGE                                                              RUBBER    I       II       III    IV                                          ______________________________________                                        Polymer C 59      (64)     (63)   (59)                                        Polymer B 73      (76) 67  (70)   (64) 72                                     Polymer A 84      (80/72)  (78/75)                                                                              (78/75) 85/75                                                 84/79    77                                                 ______________________________________                                    

The crosslinked products prepared as described were found to have thefollowing additional properties:

The crosslinked densities were not measured on all samples shown inTable 3. On average, the following values were obtained:

    ______________________________________                                                                 .sup.(1) MOLECULAR WT.                                                        BETWEEN                                              RUBBER  CROSSLINK DENSITY                                                                              CROSSLINKS                                           ______________________________________                                        Polymer C                                                                             0.09 × 10.sup.-4 moles/cm.sup.3                                                          Mc = 51,000                                          Polymer B                                                                             0.12 × 10.sup.-4 moles/cm.sup.3                                                          Mc = 38,000                                          Polymer A                                                                             0.15 × 10.sup.-4 moles/cm.sup.3                                                          Mc = 32,000                                          ______________________________________                                         .sup.(1) M.sub.c was calculated by the equation:                              ##STR1##                                                                 

As can be seen from the data in the Tables, it is possible tomanufacture elastomeric polymers having low levels of crosslinking,i.e., partially crosslinked polymers in a controlled manner to avoidsignificant fluctuation in products such as the fluctuations produced bymethods of the prior art.

EXAMPLE 2 Use in sealing tape formulations

A sealing tape formulation was prepared by using a partially crosslinkedbutyl product produced in accordance with Example 1. The formulation wasas follows:

    ______________________________________                                                        Parts by weight                                               ______________________________________                                        Partially crosslinked Butyl                                                                     100                                                         CaCO.sub.3 (Calofort U)                                                                         235                                                         Silicate (Zeosil 35)                                                                             60                                                         Escorez ® 1310.sup.(1)                                                                       12                                                         Parapol ® 2225.sup.(2)                                                                      150                                                         ZnO                12                                                         Irganox ® 1076.sup.(3)                                                                       1                                                          ______________________________________                                         Footnotes:                                                                    .sup.(1) Escorez 1310 is an aliphatic hydrocarbon tackyfing resin.            .sup.(2) Parapol 2225 is isobutenebutene low molecular weight copolymer.      .sup.(3) Irganox 1076 (CibaGeigy) is octadecyl3-(3,5-ditert butyl hydroxy     hydrocinnamate; an antioxidant and thermal stabilizer.                   

The formulation was made in a Z-blade mixer under nitrogen blanket at150° C., by the following sequence:

    ______________________________________                                        Time          ADD                                                             ______________________________________                                         0'           All partially crosslinked Butyl.                                10'           Escorez 1310 + Irganox 1076                                     15'           1/4 Fillers                                                     20'           1/4 Parapol 2225                                                25'           1/4 Fillers + 1/4 Parapol 2225                                  30'           1/4 Fillers + 1/4 Parapol 2225                                  35'           1/4 Parapol 2225                                                40'           1/4 Fillers                                                     90'           Dump                                                            ______________________________________                                    

The processability of the formulation was determined by measuring thestabilized torque of the mixture on a Brabender plastograph (after 15minutes). The results are shown in Table 4. In this table, theformulation designated Polymer B-IV is a composition in which the butylcomponent is Polymer B containing 0.23 wt.% chlorine produced inaccordance with Example 1, and cured with curative package IV.

                  TABLE 4                                                         ______________________________________                                                  Mooney Viscosity                                                                           Brabender Stabilized                                   Formulation                                                                             (1 + 8) at 150° C.                                                                  Torque (After 15') (Nm)                                ______________________________________                                        Polymer B 72           8.2                                                    ______________________________________                                    

The above described formulation was subjected to various tests toevaluate its performance as a sealant. The results are shown in Table 5.In addition, the tests for (a) cold flexibility at -40° C. and (b)sagging at 175° C. were performed.

                                      TABLE 5                                     __________________________________________________________________________    Formu-                                                                              Compres-                                                                             Penetra-                                                                            Yield Strength                                                                        Elonga-                                                                            BONDING TEST (Glass/Glass)                    lation                                                                              sion Set (%)                                                                         tion (mm)                                                                           (N/10 cm)                                                                             tion %                                                                             Type of Bonding                               __________________________________________________________________________    Polymer B-                                                                          75     5     84      280  adhesive                                      IV                                                                            __________________________________________________________________________

In general, good sealants require a good balance of properties whichenable (1) good accommodation of joint movements (hence low compressionset); (2) easy application (hence low softness/plasticity, e.g.,penetration of about 5 mm); avoidance of adhesive failure. Normally, theresilience and plasticity of sealants are competing properties and goodsealants are those which offer a good balance of low compression set andhigh penetration.

From Table 5, it is seen that the sealant according to the invention hasproperties which make it suitable for such uses. In addition, it has theadvantage of uniformity and consistency. The test methods used togenerate the above results were as follows:

    ______________________________________                                        Compression set  ASTM D395-85                                                                  (under constant deflection                                                    in air)                                                      Penetration      ASTM C-0782                                                  Yield strength   ASTM C-0902                                                  Elongation       ASTM D-0638                                                  ______________________________________                                    

EXAMPLE 3

An uncrosslinked chlorinated unsaturated butyl rubber comprising about0.3 weight percent chlorine was introduced into a twin screwcounter-rotating non-intermeshing extruder-reactor as follows:

1) Feed Zone: The uncrosslinked rubber entered the hopper opening andwas conveyed forward into the closed barrel section. A mixture of ZDBDC(Zinc Dibutyldithiocarbamate) and ZnO (Zinc Oxide), curing agent, in a2:1 ratio was added into the feed opening at a rate of 2.5 parts byweight per hundred of rubber (phr) (1.67 ZDBDC and 0.83 ZnO) on rubber.

2) Conveying Zone: This section was comprised of mostly simple forwardconveying flights with some interrupted flights present. Mixing in thiszone was performed at a temperature of about 120° C. to 220° C.

3) Reaction Zone: A short reaction screw is comprised of shallow channelmultiple flighted screw elements. This section was the maximum shear andmixing step in the process. At this point, the polymer temperature wasat a temperature of 180°-220° C.

4) Stripping and Venting: This section was used for degassing anyentrained air and stripping of any volatile degradation-causing productsthat may be present, such as hydrogen halides. Nitrogen was injected tosweep away any gaseous contaminants.

5) Exit Zone: This section was used for conveying the product out of theextruder-reactor.

Table 6 summarizes the process conditions and the results:

                  TABLE 6                                                         ______________________________________                                        Polymer Feed:                                                                              Chlorobutyl rubber                                                            Mooney viscosity 39 (1 + 8 at 150° C.)                                 Cl % 0.3                                                         Extruder-reactor                                                                           50 K/H feed rate                                                 Conditions   95 RPM                                                                        1.25 K/H ZDBDC/ZnO (2:1)                                                      200° C. MAX REACTION ZONE                                              TEMPERATURE                                                                   1 K/H Cocurrent stripping nitrogen                               ______________________________________                                         Footnotes:                                                                    K/H denotes kilograms per hour                                                RPM denotes revolutions per minute.                                      

What is claimed is:
 1. A partially crosslinked, unsaturated copolymer ofa C₄ to C₇ isomonoolefin and a C₄ to C₁₄ conjugated multiolefin,comprising substantially randomly distributed covalent crosslinks, anolefinic unsaturation ranging from about 0.05 to about 5.0 mole percent,a gel content ranging from about 10 weight percent to about 90 weightpercent, as measured in cyclohexane for 48 hours at a temperature of 23°C., said crosslinks having been formed after the polymerization andhalogenation of the corresponding uncrosslinked copolymer of a C₄ to C₇isomonoolefin and a C₄ to C₁₄ conjugated multiolefin, said crosslinkedunsaturated copolymer being substantially free of chemically boundhalogen, and having a crosslink density ranging from about 0.05 to0.22×10⁻⁴ moles per cubic centimeter.
 2. The partially crosslinkedunsaturated copolymer of claim 1, wherein said olefinic unsaturationranges from about 0.50 to about 2.5 mole percent.
 3. The partiallycrosslinked unsaturated copolymer of claim 1, wherein said gel contentranges from about 10 to about 89 percent.
 4. The partially crosslinked,unsaturated copolymer of claim 1, wherein said copolymer is a copolymerof isobutylene and isoprene.
 5. The partially crosslinked copolymer ofclaim 1, wherein said crosslinks are formed by reaction of a curingagent with an allylic halogen of a halogenated copolymer of a C₄ to C₇isomonoolefin and a conjugated C₄ to C₁₄ conjugated multiolefin.
 6. Thepartially crosslinked copolymer of claim 1, wherein said crosslinkedcopolymer comprises less than about 0.1 weight percent chemically boundhalogen.